1. Field of the Invention
The invention relates to the fabrication methods of a mass flow controller (MFC), and more particularly, to the methods of manufacturing an integrated MFC module which has both microvalve and mass flow sensing regions on a single semiconductor substrate.
2. Description of the Prior Art
There are a number of sensing applications currently used to sense as well as precisely control the amount of tiny mass flow in a system that is typically in the order of ml/min for gas flow and in the order of .mu.l/min for liquid flow. The linear dimensions of these devices which are in the order of cm offer the advantages of power saving, fast response and compact volume. In semiconductor fabricating processes, MFC plays an important role to precisely control the mass flow of gases or fluids in a system. Conventionally, the components of a MFC sensor are built individually and then installed together. For example, gas flow valves are usually employed electromagnetic or piezoresistive controlled valves. Flow sensors such as pressure difference, electromagnetic waves, ultrasonic or heat senescing types are often used. In the aspect for the design and manufacture of a MFC sensor, how to build those parts and incorporated on a substrate is the key technique for precision measurement. Therefore, this approach is unable to be practically mass-produced high quality MFC sensors.
Recent development trends of MFC device are integrated sensors, actuators, and controllers all in a single chip. For example, Both U.S. Pat. No. 4,808,009 to Sittler et al. and U.S. Pat. No. 5,201,221 to Forgacs et al. (the entire disclosures of which are herein incorporated by reference) disclosed integrated flow sensor structures built on a silicon substrate. However, they are somewhat different from the exact MFC structure and the fabricating process of the present invention disclosed herein.
The present invention discloses a novel integrated MFC sensor structure and the fabrication process which combines both microvalve and mass flow sensing regions on a single semiconductor substrate.